1. Field of the Invention
The present invention relates to a closure for closing a neck opening of a container and of the type comprising a cap member having a flat annular top wall with a central opening and a skirt depending from the outer periphery of the top wall, and a cover member overlying the central opening of the cap member and including a connecting portion sealingly engaging with the inner edge of the cap member.
Closures of that type may in principle be used in connection with bottles or containers of any type. Up till now, however, they have normally been used in connection with ampoules or bottles containing a pharmaceutical liquid. The closure is then used partly for retaining a perforatable stopper or disc in the neck opening of the container or bottle, and partly for maintaining the outer surface of the perforatable stopper or disc in a sterile condition till the content of the bottle or container is to be used. At that time the cover member may be removed or torn from the cap member which is fastened to the neck of the bottle or container, whereby part of the perforatable disc or stopper is laid open.
2. Description of the Prior Art
The prior art comprises two fundamentally different closures of the above type. Thus, U.S. Pat. No. 3,193,128 discloses a closure in which the connection between the inner rim portion of the cap member and the removable cover member is of such a type that when the cover member is removed from the cap member, the cover member is torn along the inner edge of the cap member so that a peripheral part of the cover member clamped between the inner edge of the cap member and the perforatable stopper or disc arranged in said neck opening of the container, remains on the container or bottle. German "Offenlegungsschrift" No. 20 40 937 discloses a closure of the other type in which the inner rim portion of the cap member is connected to the cover member in such a manner that the cover member may be removed from the container in its entirety.
In the last mentioned of these known closure types the annular top wall or end wall of the cap member is substantially plane, and the inner rim portion of the annular top wall is sealingly received in an annular channel formed in the adjacent part of the cover member. Bottles or containers provided with closures of the type in question often have to be treated in an autoclave, and in that case the closure is influenced by a substantial overpressure generated within the container or bottle. This overpressure causes the top wall or end wall of the closure to bulge outwardly. In closures of the last mentioned known type in which the annular top wall of the cap member is substantially plane such outward bulge tends to increase the diameter of the central opening in the cap member and to decrease the diameter of the bottom wall of the annular channel formed in the cover member. Consequently, treatment in an autoclave may cause a leakage of the connection between the inner rim portion of the cap member and the cover member so that the perforatable stopper or disc is unintentionally contaminated prior to removal of the protecting cover member. It may even happen that the cover member is completely or partly pushed off during or in connection with processing of the containers in or removal of the containers from an autoclave. The fact that the cap member and the cover member are normally made from different materials having different coefficients of expansion, such as metal and plastic or rubber, respectively, increases the risk of leakage in connection with the described known closure.